Starch is a complex carbohydrate often found in the human diet. The structure of starch is glucose polymers linked by α-1,4 and α-1,6 glucosidic bonds. Commercially, glucoamylases are used to further hydrolyze cornstarch, which has already been partially hydrolyzed with an alpha-amylase. The most widely utilized glucoamylase is produced from the fungus Aspergillus niger; one of the problems with the commercial use of this enzyme is its relatively low thermostability.
In general, starch to fructose processing consists of four steps: liquefaction of granular starch, saccharification of the liquefied starch into dextrose, purification, and isomerization to fructose. The object of a starch liquefaction process is to convert a concentrated suspension of starch polymer granules into a solution of soluble shorter chain length dextrins of low viscosity. This step is essential for convenient handling with standard equipment and for efficient conversion to glucose or other sugars. To liquefy granular starch, it is necessary to gelatinize the granules by raising the temperature of the granular starch to over about 72° C. The heating process instantaneously disrupts the insoluble starch granules to produce a water soluble starch solution. The solubilized starch solution is then liquefied by amylase. A starch granule is composed of: 69-74% amylopectin, 26-31% amylose, 11-14% water, 0.2-0.4% protein, 0.5-0.9% lipid, 0.05-0.1% ash, 0.02-0.03% phosphorus, 0.1% pentosan. Approximately 70% of a granule is amorphous and 30% is crystalline.
Staling of baked products (such as bread) has been recognized as a problem which becomes more serious as more time lies between the moment of preparation of the bread product and the moment of consumption. The term staling is used to describe changes undesirable to the consumer in the properties of the bread product after leaving the oven, such as an increase of the firmness of the crumb, a decrease of the elasticity of the crumb, and changes in the crust, which becomes tough and leathery. The firmness of the bread crumb increases further during storage up to a level, which is considered as negative. The increase in crumb firmness, which is considered as the most important aspect of staling, is recognized by the consumer a long time before the bread product has otherwise become unsuitable for consumption.
There is a need in the industry for new amylases, e.g., acid amylases, useful for various uses including commercial cornstarch liquefaction processes or improved manufacturing having new or improved performance characteristics over the industry standard enzymes, e.g., from Bacillus licheniformis. There is also an industry drive to identify amylases and glucoamylases capable of efficiently hydrolyzing granular starch (e.g. raw granular starch) at low temperatures without the need for a high temperature starch gelatinization step; the enzymes of the invention, e.g. amylases, glucoamylases and glucosidases, can be utilized to fulfill this need.
There is also a need for new amylases having utility in automatic dish wash (ADW) products and laundry detergent. In ADW products, the amylase will function at pH 10-11 and at 45-60° C. in the presence of calcium chelators and oxidative conditions. For laundry, activity at pH 9-10 and 40° C. in the appropriate detergent matrix will be required. Amylases are also useful in textile desizing, brewing processes, starch modification in the paper and pulp industry and other processes described in the art.